The incidence of respiratory distress syndrome (RDS) is increased almost sixfold in infants of diabetic mothers (IDM), even when suitable corrections are made for gestational age. IDMs experience hyperinsulinemia both in utero and in the postnatal period as a result of intrauterine hyperglycemia, particularly when maternal glucose homeostasis is poorly controlled. We propose to examine the hypothesis that hyperinsulinemia secondary to hyperglycemia alters fetal lung maturation using both in vivo and in vitro studies. In vivo studies: Exogenous glucose will be infused into chronically catheterised fetal lambs from which tracheal fluid can be continuously collected. Surface activity of the tracheal fluid will be assayed on a surface balance and surfactant concentration and flux in tracheal fluid will be quantified. Lipid analysis of the tracheal fluid will be carried out in order to delineate surfactant composition. Respiratory surface area and the stability index of lungs will be derived from pressure-volume curves of excised lungs. Insulin, cortisol, beta-sympathomimetic, and thyroid hormone receptors will be assayed in nuclear and cytoplasmic fractions of whole lung homogenates. In vitro studies: Alveolar type II cells (greater than 95% purity) and lung fibroblasts (greater than 95% purity) will be separated from organotypic cultures of fetal rabbit lungs (26-31 days gestation) and grown in monolayer culture using Warburton's modification of Douglas' and Sevanian's methods. These preparations will be used to simulate and study the effects of the IDM's fetal environment on interactions between lung cells in three groups of experiments: 1. Effects of fibroblast conditioned media (FCM) prepared with insulin, cortisol, isoxuprine and/or propranolol, and thyroid hormone exposed fibroblasts on growth (3H thymidine DNA incorporation), metabolic rate (14CO2 production) and surfactant synthesis and release (3H choline and 3H myo-inositol incorporation) by alveolar type II cells in comparison with directly treated type II cells. 2. Effects of above FCM on cortisol, insulin, beta-sympathominetic and thyroid hormone receptors in alveolar type II cells. 3. Elaboration of extracellular matrix by lung fibroblasts, its composition and its effects on alveolar type II cell growth, metabolic rate and surfactant production will be studied. In addition, modification of extracellular matrix production by insulin, glucose and cortisol will be studied.